Influence of microwave-assisted hydrothermal treatment time on the crystallinity,morphology and optical properties of ZnWO4 nanoparticles: Photocatalytic activity

In this work, zinc tungstate (ZnWO₄) nanoparticles were obtained by microwave-assisted hydrothermal method at 140 °C and 2 atm. The hydrothermal treatment time was varied at 0, 5, 10, 30, 60 and 120 min. The nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM), X-ray fluorescence (FRX), nitrogen adsorption by Brunauer-Emmett-Teller method (BET), UV–Visible spectroscopy (UV–Vis) and Photoluminescence (PL) properties. The adsorptive and photocatalytic properties were estimated against methylene blue (MB - cationic) and methyl orange (MO - anionic) dyes. The diffractograms show that the larger hydrothermal treatment time, anhigher the powders crystallinity. The BET and SEM analysis indicate that the increase in hydrothermal time does not interfere significantly in nanoparticles size but reduces their porosity. The change in the surface area is consistent with the adsorption tests, where the increase of the hydrothermal treatment time reduces the adsorption against the MB and MO dyes. However, increasing the hydrothermal treatment time provides an increase in photocatalytic activity.     

Bio-inspired ZnS quantum dots as efficient photo catalysts for the degradation of methylene blue in aqueous phase

ZnS quantum dots are semiconductor nanoparticles characterized by superior optoelectronic properties. The amenability of these nanoparticles in initiating efficient photo-redox reactions enable their use as photocatalysts for environmental remediation. In the present study, ZnS quantum dots were biosynthesized from Zn tolerant Penicillium sp. under ambient reaction conditions. The biogenic ZnS quantum dots were characterized using TEM, SEM, XRD, FTIR and UV–Vis absorption studies that revealed the formation of spherical particles of average diameter 11.08?nm with a zinc blend crystal structure and the optical properties were in par with chemically synthesized ZnS. The biogenic ZnS were then used for the photodegradation of methylene blue (MB) dye. It was found that the green synthesized ZnS quantum dots exhibited good photocatalytic activity with a half-life of 4?h. Further, the dye degradation efficiency was enhanced as the ZnS nanocatalyst/dye ratio increased and reached equilibrium within 6?h. The present study reports an inexpensive and scalable method to fabricate ZnS nano hybrids with practical applicability in the remediation of pollutants in textile, paper and dyeing industry.     

超声-S/TiO_2纳米颗粒可见光催化协同降解亚甲基蓝

采用共沉淀-浸渍法制备掺杂S的TiO2光催化剂,利用XRD,TEM,UV-Vis-DRs,XPS等方法对其结构、元素组成和光谱学特征进行研究,以亚甲基蓝(MB)的光催化降解反应为模型,探讨高效利用可见光降解亚甲基蓝的反应体系。实验结果表明,S掺杂最佳热处理温度为500℃。掺杂光催化剂晶型仍为锐钛矿型,其粒径变小,比表面积增大,热稳定性增加,对可见光的吸收增强。超声波对光催化降解反应有协同作用,S/TiO2在可见光下对亚甲基蓝的降解率明显高于纯TiO2。     

Green synthesis of Ni@Fe3O4 and CuO nanoparticles using Euphorbia maculata extract as photocatalysts for the degradation of organic pollutants under UV-irradiation

This paper presents a fast, biogenic and green method for the synthesis of highly stable and small sized metal nanoparticles (MNPs). This technique has some benefits compared to the conventional physical and chemical methods. It is simple, rapid, cheap and environmentally friendly. In addition, it does not require any costly or hazardous chemicals. The extracts of Euphorbia maculata aerial parts were used in a green synthesis method in order to prepare magnetic Ni@Fe₃O₄ and CuO NPs. Fourier transforms infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), ultraviolet–visible (UV–Vis), energy dispersive X-ray spectrometry (EDS), Brunauer-Emmett-Teller (BET) and thermo gravimetric-differential thermal analysis (TGA) analytical techniques were used for analyzing the green synthesized compounds. The photocatalytic activity of the synthesized NPs was tested in the degradation of different organic dye pollutants such as congo red (CR), methylene blue (MB) and Rhodamine B (RhB) under UV irradiation. The effects of different parameters such as nanoparticle dosage, contact time, pH, and initial dye concentrations on the capacity of the photocatalyst adsorption were also studied. The comparison of the photocatalytic activity of the biosynthesized nanoparticles reveals that the catalytic activity of CuO NPs is higher than that of Ni@Fe₃O₄ NPs. Furthermore, good photocatalytic stability of the NPs in the degradation of MB under UV light irradiation was observed after the recycling. The photocatalyst efficiency did not considerably change after four cycles, which indicated excellent photocatalytic stability.     

Polymer-assisted freeze-drying synthesis of Ag-doped ZnO nanoparticles with enhanced photocatalytic activity

Ag-doped ZnO nanoparticles with high and stable photocatalytic activity were prepared by polymer-assisted freeze-drying method with simple process and without organic solvents used. The structural morphology and optical properties of Ag-doped ZnO nanoparticles were characterized by X-ray Diffraction (XRD), Inductive Coupled Plasma Optical Emission Spectrometry (ICP-OES), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and high resolution TEM (HRTEM) with energy dispersive X-ray spectroscopy, Ultraviolet-visible Diffuse Reflectance Spectroscopy (UV–vis DRS), X-ray Photoelectron Spectroscopy (XPS) and Fourier Transmission Infrared Spectroscopy (FTIR). Moreover, the thermoanalytical measurements (TGA–DTG) analysis is carried out for proper calcination temperature. XRD results show that Ag nanoparticles were successfully doped into ZnO lattice, and UV–vis DRS results indicate that the doped Ag nanoparticles result in ZnO exhibiting enhanced light trapping capability in the 400?nm and 600?nm range. The photocatalytic activity of Ag-doped ZnO was examined by analyzing the degradation of methyl orange (MO) and methylene blue (MB) dyes under UV light and solar light irradiation, and the results show that all Ag-doped ZnO nanoparticles exhibit better photocatalytic activity than those of pure ZnO nanoparticles at the same degradation conditions; especially the synthesized Ag-ZnO nanoparticles are easy to be recycled and have high photocatalytic stability. Based on the experimental results, the photocatalytic electron transfer path and the photocatalytic mechanism of Ag-ZnO nanoparticles under UV and solar irradiation conditions are explained and clarified.     

Preparation of aerochitin‐TiO2 composite for efficient photocatalytic degradation of methylene blue

An aerochitin–titania (TiO₂) composite was successfully synthesized and characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, field emission scanning electron microscopy, and N₂ adsorption isotherms. The photocatalytic activity of the composite was investigated on the degradation of the model organic pollutant, methylene blue (MB) dye, under UV irradiation. The aerochitin–TiO₂ composite showed excellent adsorptive and photocatalytic activity with a degradation degree of 98% for MB. The first‐order rate constants for the photodegradation MB by TiO₂ nanoparticles and aerochitin–TiO₂ composite were found to be (3.49 ± 0.04) × 10^?3 and (1.82 ± 0.02) × 10^?2 min^?1. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45908.     

Adsorption of Anionic and Cationic Dyes from Aqueous Solution on Non-Calcined Mg-Al Layered Double Hydroxide: Experimental and Theoretical Study

Non-calcined Mg-Al layered double hydroxide (LDH) with Mg/Al molar ratio of 3:1 was synthesized using the co-precipitation method. Sorption of anionic (acid blue 25 - AB25, reactive blue 4 - RB4), and cationic (methylene blue - MB) dyes by Mg-Al LDH form aqueous solution was investigated. The effect of solution pH, initial concentration, and contact time were investigated by batch adsorption experiments. The adsorbed amount increases with decrease in pH solution for AB25 and RB4. The cationic dye (MB) solution was insensitive to pH variation and also exhibited a low performance in the kinetic equilibrium studies. While anionic dyes were almost completely extracted from the solution, 90% of the methylene blue remained in solution. The equilibrium data were well described using the Langmuir-Freundlich model for RB4, AB25, and MB dyes with maximum adsorption capacity of 328.90, 246.10, and 43.48 mg/g, respectively. Finally, the mechanism of adsorption involving the dyes and LDH was evaluated using the Monte Carlo approach in the NVT ensemble. The results suggest that molecular simulation can be used to preview quantitatively the dye uptake. Supplemental materials are available for this article. Go to the publisher's online edition of Separation Science & Technology to view the supplemental file.     

PMAA／HEC核-壳聚合物纳米微球对亚甲基蓝负载和释放行为研究

以羟乙基纤维素（HEC）和甲基丙烯酸（MAA）为原料,采用模板聚合方法制备了核-壳聚合物纳米微球。采用可见分光光度法,研究了该纳米微球对亚甲基蓝（MB）模型分子的负载容量及释放行为,并用粒径-电位仪和透射电镜对负载MB前后的纳米微球进行了表征。结果表明：纳米微球负载MB的容量主要依赖于微球中PMAA组分的含量以及介质的pH值;负载微球的释放速率具有pH依赖性,可以通过改变介质的pH值实现MB的可控释放。     

Effect of modified graphene quantum dots on photocatalytic degradation property

The effective use of solar energy in sewage disposal has been extensively investigated. This work focuses on the photocatalytic property of graphene quantum dots (GQDs) and polymer-modified GQDs under visible light. A hydrothermal synthesis route to GQDs was developed by using citric acid as a carbon precursor. The GQDs were modified with polyethylenimine (PEI) and polyethylene glycol (PEG). The obtained GQDs, GQDs-PEIs, and GQDs-PEGs were characterized and their structural information was determined through Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), photoluminescence spectroscopy, and UV–Vis absorption spectroscopy. Results revealed that the GQDs were uniform in size (2–5 nm) and rich in oxygen-containing groups. The GQDs exhibited a strong blue and excitation-independent photoluminescent behavior under excitation wavelengths of 320–420 nm. The photocatalytic performance of these samples was demonstrated on the basis of methylene blue (MB) degradation. The photocatalytic rates of GQDs, GQDs-PEIs, and GQDs-PEGs decreased successively. The polymer-modified GQDs could qualitatively control the degradation rate of MB. Free radical species were generated to oxidize MB under light irradiation. Thus, photocatalytic organic matter degradation, sustained drug release, and tracking can be combined to implement proper sewage disposal.Prime noveltyThe main object of this work is to find out a novel property of graphene quantum dots (GQDs) as efficient nanomaterials for degradation of organic pollutant dyes under visible light irradiation. And, the GQDs exhibited a strong blue and excitation-independent photoluminescent behavior under excitation wavelengths of 320–420 nm. Moreover, the degradation rate could be qualitatively controlled by using different polymer-modified GQDs. Thus, photocatalytic organic matter degradation, sustained drug release, and tracking can be combined to implement proper sewage disposal. Also, the degradation mechanism is discussed.     

Adsorption of selected dyes on Ti3C2Tx MXene and Al-based metal-organic framework

MXene and metal organic framework (MOF) were used as the main adsorbents to remove synthetic dyes from model wastewater. Methylene blue (MB) and acid blue 80 (AB) were used as the model cationic and anionic synthetic dyes, respectively. To investigate the physicochemical properties of the adsorbents used, we carried out several characterizations using microscopy, powder X-ray diffraction, a porosimetry, and a zeta potential analyzer. The surface area of MXene and MOF was 9 and 630 m² g⁻¹, respectively, and their respective isoelectric points were approximately pH 3 and 9. Thus, MXene and MOF exhibited high capacity for MB (~140 mg g⁻¹) and AB (~200 mg g⁻¹) adsorption, respectively due to their electrostatic attractions when the concentrations of the adsorbents and adsorbates were 25 and 10 mg L⁻¹. Furthermore, the MOF was able to capture the MB due mainly to hydrophobic interactions. In terms of the advantages of each adsorbent according to our experimental results, MXene exhibited fast kinetics and high selectivity. Meanwhile, the MOF had a high adsorption capacity for both MB and AB. The adsorption mechanisms of both adsorbents for the removal of MB and AB were clearly explained by the results of our analyses of solution pH, ionic strength, and the presence of divalent cation, anion, or humic acids, as well as other characterizations (i.e., Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy). According to our results, MOF and MXene can be used as economical treatments for wastewater containing organic pollutants regardless of charge (e.g., MB and AB), and positively charged one (e.g., MB), respectively.     

纳米ZnO/膨润土光催化降解亚甲基蓝研究

以Zn(NO3)2和膨润土为原料,采用沉淀法制备纳米ZnO-膨润土复合光催化材料,用FT-IR、XRD和SEM对其结构和形貌进行了表征。以高压汞灯为光源,光催化降解活性亚甲基蓝模拟染料废水,研究了ZnO/有机膨润土光催化降解性能,讨论了影响亚甲基蓝降解率主要因素。结果表明,在光照射下1.5 h,ZnO/膨润土光催化降解亚甲基蓝达96%,其重复使用降解效果保持稳定,利用该复合光催化材料降解有机染料废水是一种可行的方法。     

DyCrxFe(1-x)O3 nanoparticles prepared by wet chemical technique for photocatalytic applications

DyCr_xFe_(1-x)O₃ (0 ≤ x ≥ 0.4) nanoparticles were prepared using facile chemical route. Structural and morphological evaluation was carried out using X-ray diffraction (XRD) and electron microscopy. Formation of orthorhombic DyFeO₃ nanoparticles was confirmed by XRD with crystallite size of 9–10 nm. FESEM images revealed nearly spherical morphology of the fabricated nanoparticles. Energy dispersive X-ray (EDX) technique was employed to confirm the presence of Dy, Cr, Fe and O elements in DyCr_xFe_(1-x)O₃ nanoparticles. FTIR studies illustrated the presence of characteristics stretching and bending vibrations. UV–visible spectroscopy was used to analyze the photocatalytic performance of the DyFeO₃ and Cr-substituted DyFeO₃ nanoparticles and optical band gap measurements. Photocatalytic activities of the prepared substituted and un-substituted DyFeO₃ nanoparticles were conducted using three different dyes. These dyes were (i) methyl orange, (ii) rhodamine B and (iii) methylene blue. Lower band gap and higher photocatalytic performance was observed for Cr-substituted DyFeO₃ nanoparticles with methylene blue dye.     

Improved photocatalytic performance of Gd and Nd co-doped ZnO nanorods for the degradation of methylene blue

This paper reports the synthesis of pure ZnO, Gd and Nd co-doped ZnO nanorods based nanocomposites via simple hydrothermal method. Subsequently, the prepared photocatalysts were characterized using XRD, SEM/EDX, TEM, UV–visible and PL spectroscopy. The XRD results demonstrate that Gd and Nd ions were incorporated into ZnO lattice in the synthesized ZnO based nanocomposites and showed hexagonal wurtzite structure. The SEM and TEM results show that nanorods having nanoscale diameter and length were successfully synthesized by hydrothermal method. The UV–visible spectroscopy verified that the band gap of ZnO was reduced due to incorporation of Gd and Nd into ZnO photocatalyst. Similarly, Gd and Nd incorporation into ZnO was found effective to reduce the recombination of electrons and holes as confirmed by PL spectroscopy. Moreover, the prepared nanocomposites with various atomic ratios (0.5–2%) were tested for photocatalytic degradation of methylene blue (MB), under visible light irradiation. The highly efficient and optimized 1.5% Nd/ZnO nanocomposite demonstrated enhanced photocatalytic performance for the degradation of methylene blue compared to pure ZnO and other nanocomposites. Furthermore, the recycling results show that the 1.5% Nd/ZnO nanocomposites displayed good stability and long-term durability. These finding suggest that the ZnO based nanocomposite could be efficiently used in various energy and environmental applications.     

Preparation of Ag nanoparticles loaded TiO2 nanoplate arrays on activated carbon fibers with enhanced photocatalytic activity

Ag loaded TiO₂ nanoplate array which grew on activated carbon fiber (ACF) was prepared in the present work. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis diffuse reflectance spectra (DRS). The photocatalytic degradation of methylene blue (MB) was used to investigate the activity of the synthesized samples. Under both UV and visible light irradiation, the Ag loaded samples showed enhanced photocatalytic activity. Besides, the effect of the deposition dosage of Ag nanoparticles on the photocatalytic activity was also investigated. Under UV light irradiation, the Ag nanoparticles acted as electron traps, which enhanced electron–hole separation efficiency of TiO₂. Under visible light irradiation, the Ag nanoparticles showed surface plasmon resonance, which induced the visible light responsive photocatalytic activity for the obtained samples.     

铁掺杂氧化锌制备及对有机染料的光催化降解

采用沉淀法制备铁掺杂的纳米氧化锌。通过粉末X射线衍射（PXRD）和红外光谱（IR）对样品及其前驱体进行表征;采用分光光度计测定样品光催化降解有机染料的效果;用扫描电子显微镜（SEM）观测样品的表面形貌。实验结果表明,铁掺杂的氧化锌比纯氧化锌具有更高的催化活性和催化效率。这归因于铁均匀分布在氧化锌中,避免了氧化锌纳米粒子间的团聚,改善了氧化锌表面的性质,在降解有机染料过程中与有机染料大面积接触,对甲基橙和亚甲基蓝具有良好的降解效果,是一种有潜力的光催化降解材料。     

Enhancement in the photocatalytic and antimicrobial properties of ZnO nanoparticles by structural variations and energy bandgap tuning through Fe and Co co-doping

In this study, pure ZnO and iron (Fe) and cobalt (Co) co-doped ZnO nanoparticles were synthesized by varying Fe and Co concentrations using the co-precipitation method. The physical properties of as-prepared samples were investigated through XRD, FTIR, SEM, and UV–vis spectroscopy. X-ray diffraction confirmed the strong influence of Fe and Co ions on structural parameters without disturbing the basic ZnO hexagonal structure. The microstructural study was executed by using the Scherrer, W–H, and SSP methods. FTIR confirmed the presence of Zn–O, and Zn–M–O (M = Fe, Co) vibrational modes, which further confirmed the successful incorporation of dopants ions. The energy bandgap (E_g) extracted from UV–vis spectra has shown red-shift (3.37–2.7 eV) for decreasing Fe contents, whereas blue-shift (3.37–3.39 eV) for increasing Co concentration. SEM was used to investigate surface morphology, which represents the high rate of agglomeration. The photocatalytic test was performed on grown samples against various dyes and also observed the effects of varying concentrations of Fe and Co ions. The maximum degradation efficiency (98.8%) at 6%Fe and 4%Co under direct sunlight in 60 min against methylene blue (MB) was achieved. The photocatalytic activity of optimized concentration (6%Fe and 4%Co) was further tested against cresol red (CR), methyl orange (MO), safranin-O (SO), rhodamine-B (RhB), and methyl red (MR) dyes. The maximum degradation efficiency against MR dye (96.0%) was observed. The antibacterial test against Staphylococcus aureus and Klebsiella pneumoniae bacterial strains have shown that co-doped ZnO nanoparticles have a higher activity as compared to pristine ZnO, and furthermore, the sample with 6%Fe and 4%Co concentration exposed the highest antibacterial actively for both bacterial strains.     

Fabrication of novel SnWO4/ZnO using Muntingia calabura L. leaf extract with enhanced photocatalytic methylene blue degradation under visible light irradiation

In this study, SnWO₄/ZnO heterostructure has been successfully constructed using Muntingia calabura L. leaf extract (MCE). We conducted phytochemical tests to qualitatively detect the presence of secondary metabolites such as alkaloids, saponins, flavonoids, and tannins, which play an essential role in the formation of SnWO₄/ZnO. The photocatalytic activities of pristine SnWO₄, pristine ZnO, and SnWO₄/ZnO heterostructure were evaluated for the degradation of methylene blue (MB) under visible light irradiation. To investigate the photocatalytic activity of SnWO₄/ZnO heterostructure in the visible region, the adsorption effect of SnWO₄/ZnO was also studied. SnWO₄/ZnO heterostructure shows the highest degradation percentage of 82.86% within 120 min compared to pristine SnWO₄ and ZnO, which exhibit the degradation percentage of 69.48 and 40.41%, respectively. The enhanced photocatalytic of MB degradation is attributed to the formation of SnWO₄/ZnO heterostructure as a result of the decreased optical bandgap from 3.06 to 2.68 eV due to the low recombination rate of photogenerated electron-hole pairs. SnWO₄/ZnO shows a remarkable photocatalyst for dyes degradation with remarkable stability after four consecutive cycles. Importantly, this work demonstrates a simple eco-friendly, and low-cost green synthesis method to produce SnWO₄/ZnO with excellent photocatalytic activity and stability for dyes degradation under visible light irradiation.     

Photocatalytic activities of electrospun tin oxide doped titanium dioxide nanofibers

SnO₂ doped TiO₂ electropsun nanofiber photocatalysts were successfully prepared by means of electrospinning process. The surface morphology, structure and optical properties of the resultant products were characterized by field-emission electron microscopy (FE-SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy, photoluminescence (PL) and cathodoluminescence (CL) techniques. The utilized physiochemical analyses indicated that the introduced SnO₂ doped TiO₂ nanofibers have a smooth surface and uniform diameters along their lengths. The photocatalytic performance of the composite nanofibers was tested for degradation of methylene blue (MB) and methyl orange (MO) dye solution under ultraviolet (UV) irradiation. Under the UV irradiation, the photocatalytic reaction rate in case of utilizing SnO₂-doped TiO₂ nanofibers was rapidly increased than that of the pristine TiO₂ nanofibers. Overall, this study demonstrates cheap, stable and effective material for photocatalytic degradation at room temperature.     

The comparative study of photocatalytic self‐cleaning properties of synthesized nanoscale titania and zirconia onto polyacrylonitrile fibers

The photocatalytic activity of TiO₂ and ZrO₂‐coated polyacrylonitrile (PAN) fibers was compared through the self‐cleaning of methylene blue and eosin yellowish. TiO₂ and ZrO₂ nanocrystals were successfully synthesized and deposited onto PAN fibers with photocatalytic self‐cleaning activity using the sol‐gel process at low temperature. The pristine and treated samples have been characterized by several techniques, such as scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, diffuse reflectance spectroscopy, X‐ray diffraction, and thermogravimetric analysis. The TiO₂ nanoparticles with 10–20 nm in size, and ZrO₂ with 20–40 nm have been synthesized to form dispersed particles on the fiber surface, which shows photocatalytic properties when exposed to UV–Vis light. The photocatalytic activity, tested by measuring the degradation of adsorbed methylene blue and Eosin Y. Photocatalytic activity of TiO₂‐coated fibers toward dyes degradation was higher than that of ZrO₂‐coated fibers. This preparation technique can be also applied to new fabrics to create self‐cleaning and UV irradiation protection properties in them. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Determination of the photocatalytic efficiency of TiO2 coatings on ceramic tiles by monitoring the photodegradation of organic dyes

A method for the evaluation of the photocatalytic effectiveness of nanotitania coatings on ceramic substrate was established. Decolourization of three organic dyes, including methylene blue (MB), rhodamine B (RB) and crystal violet (CV), was investigated under different experimental conditions. The results showed that the UV light spectrum and light intensity are important parameters when establishing this method.The effect of TiO₂ on the percentage degradation of the dyes was examined by varying its concentration in the suspensions between 0.1% and 4.5 wt%, which resulted in different thicknesses of the TiO₂ layers, and as expected higher percentages of nanotitania resulted in higher photocatalytic efficiencies. However higher amounts of titania lead to the formation of cracks on the surface, which might detrimentally affect adhesion and thus also long-term durability. The applicability of all the dyes used in the present study was proved, and there is good correlation between MB, RB and CV in the evaluation of self-cleaning efficiency.